Genistein is a polyphenolic molecule and the active form of the soy isoflavone genistin. It has both phytoestrogen and protein tyrosine kinase inhibiting properties. Since tyrosine phosphorylation is involved in central nervous system regulation of neurotransmission inhibition, genistein may be a novel strategy to directly modulate synaptic activity and treat neuropsychiatric illnesses. Genistein?s specific hormonal properties may also have salutary effects on brain function in depressed patients. Genistein increases dopamine and other monoamine activity, affects neurotrophic factor transcription, and has neuroprotective properties. This is an 8-week double blind parallel study that will examine the efficacy and safety of Novasoy, a marketed botanical dietary supplement, in male and female patients, ages 18 and over, with a diagnosis of major depression (without psychotic features) (n=60 in each group). The study has two Study Periods. Study Period I is the washout phase (1 week) and evaluation period. Study Period II is a monotherapy 8-week parallel, placebo controlled, acute treatment phase in which the efficacy and tolerability of isoflavones is compared to baseline. Subjects will be randomized 1:1 with stratification for sex. Improvement in depressive symptoms is hypothesized to be significantly greater in the active soy isoflavone group. At this point 13 depressed patients have been randomized into the study.